staging: lustre: add ability to migrate inodes.

Add client support to migrate the individual inodes
from one MDT to another MDT, and this functionality
will only migrate inode layout on MDT but not touch
data object on OST.

The directory will be migrated from top to the bottom,
i.e. migrating parent first, then migrating the child.

Signed-off-by: wang di <di.wang@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-2430
Reviewed-on: http://review.whamcloud.com/6662


Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>